1. Field of the Invention
The present invention relates to a toner level detecting device in a unit for supplying toner to a developing unit of an image forming apparatus such as a printer, copying machine, or facsimile machine.
2. Description of the Related Art
In a known image forming apparatus, a dry development method may be used wherein development is performed by supplying toner to a development region on the surface of a photosensitive drum. As disclosed in Japanese Patent Publication No. 60-2660, such an image forming apparatus may include a casing of a developing unit; a developing sleeve rotatably mounted in the casing, the developing sleeve carrying on its outer circumference a mixture of toner and magnetic carrier; and an agitator rotatably mounted in the casing for supplying toner to the developing sleeve. A magnetic roller may be enclosed in an inner-diameter portion of the developing sleeve, and the agitator may include an agitating member having a cleaning brush. Further, an L-shaped light transmitting member may be mounted inside the casing of the developing unit on one side thereof in such a manner that a light emitting surface and a light receiving surface of a photosensor for detecting a toner level are opposed to each other. The light emitting surface and the light receiving surface may be cleaned by the cleaning brush of the agitating member of the agitator.
In the related art mentioned above, however, a light emitting element and a light receiving element of the photosensor may be separately mounted so that the light emitting surface and the light receiving surface are opposed to each other. If the elements are mounted in this manner, the elements may be misaligned, and a high detection accuracy cannot be obtained.
To cope with this problem, it is known to use a photointerrupter for detecting a toner level, as shown in FIG. 9. The photointerrupter, denoted by reference numeral 100 in FIG. 9, has a light emitting element 100A and a light receiving element 100B located close to the outer wall surface of the toner supply chamber. A pair of toner detecting portions 101A and 101B project inward from a wall of the toner supply chamber so as to be interposed between the light emitting element 100A and the light receiving element 100B. The toner detecting portions 101A and 101B are connected by a connecting portion 101C, which may be integrally formed therewith, and which may be formed of a light transmitting material.
With this arrangement, light emitted from the light emitting element 100A passes through the toner detecting portion 101A, through the space between the toner detecting portions 101A and 101B, and then through the toner detecting portion 101B to finally reach the light receiving element 100B. When the toner level in the toner supply chamber is high, the light is blocked by toner between the toner detecting portions 101A and 101B. When the toner level in the toner supply chamber is low, or zero, the light is received by the light receiving element 100B.
However, as shown by an optical path 102A in FIG. 9, there is a possibility that the light from the light emitting element 100A may be repeatedly internally reflected in the toner detecting portions 101A, 101B and the connecting portion 101C such that the light is indirectly transmitted from the light emitting element 100A to the light receiving element 100B. In addition, as shown by an optical path 102B in FIG. 9, there is a possibility that the light from the light emitting element 101A may be simply reflected once on the inner bottom surface of the connecting portion 101C to reach the light receiving element 100B. Light transmitted along the optical paths 102A or 102B can cause a false detection signal indicating "low toner level" or "zero toner level" when the toner level is actually still high.